Splicing of one optical fiber to another or of one optical fiber to an optical waveguide is known. Such splicing can be done by a variety of techniques, including fusion-splicing, which involves localized melting in the region of the splice.
The following references disclose fusion-splicing of fiber to fiber or fiber to silica-waveguide: (1) R. Rivoallan et al, "Monomode fibre fusion-splicing with CO.sub.2 laser", Electronics Letters, Vol. 19, No. 2, pp.54-55, 1983; (2) R. Rivoallan et al, "Fusion-splicing of fluoride glass optical fibre with CO.sub.2 laser", Electronics Letters, Vol. 24, No. 12, pp.756-757, 1988; (3) N. Shimizu et al, "Fusion-splicing between optical circuits and optical fibres", Electronics Letters, Vol. 19, No. 3, pp.96-97, 1983; (4) T. Shiota et al, "Improved optical coupling between silica-based waveguides and optical fibers", OFC'94 Technical Digest, pp.282-283; and (5) H. Uetsuka et al, "Unique optical bidirectional module using a guided-wave multiplexer/demultiplexer", OFC'93 Technical Digest, p. 248-249. In both cases (fiber-fiber or fiber-waveguide), the masses to fuse are very small and of similar size. The fusion does not require careful thermal balance between the two components involved and can be done with a laser beam impinging from the side.
U.S. Pat. No. 4,737,006 entitled "Optical Fiber Termination Including Pure Silica Lens And Method Of Making Same", issued to K. J. Warbrick on Apr. 12, 1988, discloses fusion-splicing an undoped (pure) silica rod to a single mode fiber to fabricate a collimator, employing an electric arc. However, this is an extremely complicated method and has limited applications.
The present practice in the art often requires the attachment of optical fibers to other optical elements such as lenses, filters, gratings, prisms, and other components which have a much larger cross-sectional area than the optical fibers. The most often utilized processes for attaching optical fibers to the larger optical elements include (1) bonding the fiber faces directly to the optical element with adhesives or (2) engineering a complex mechanical housing which provides stable positioning of air-spaced fibers and optical elements throughout large changes in environmental conditions.
The use of adhesives in the optical path of such devices is undesirable due to the chance of degradation of the adhesive over time. On the other hand, spacing the fibers a fixed distance away from the optical elements by utilizing complex mechanical housings requires the use of anti-reflection coatings at all air-glass interfaces in order to minimize losses of optical energy through the device. The presence of air-glass interfaces also provides a source of back-reflected light into the optical fibers. This back-reflected light is a source of noise in many communication networks, and effectively limits transmission bandwidth of such communication networks.
In previous art, it has been shown that positioning an angle cleaved fiber or polished fiber in proximity to the angle polished face of a collimating lens results in excellent collimation and excellent performance characteristics. However, these existing technologies for assembling collimators require very labor intensive active alignment techniques. The alignment techniques include manipulating the position of the fiber relative to the lens in three linear axes and three rotational axes during final assembly. If a collimator can be built that effectively makes the fiber and the lens a single piece, then alignment can be reduced to two linear and two rotational axes during the fusion process and there is no need for alignment during final assembly, thereby reducing costs dramatically.
A key performance parameter to be minimized in collimator assemblies is back reflection of light down the fiber. By butt-coupling or fusion-splicing a fiber to a lens of the same refractive index, there is no apparent interface to cause back reflection. The beam is then allowed to diverge in the lens and does not see an index break surface until it exits the lens. By then, the beam is so diffused that the amount of light that can return to the fiber core is extremely small.
Many advances can be made in the optoelectronics and telecommunications markets if one is able to fusion-splice a single mode optical fiber directly to a collimating lens, a filter, a grating, a prism, a wavelength division multiplexer (WDM) device, or any other optical component of comparatively larger cross-sectional area. More generally, these advances can be made if one is able to fuse optical components of substantially different cross-sectional areas.
Thus, a need remains for a method of fusion-splicing optical components of significantly different cross-sectional areas.